U.S. patent application number 10/376631 was filed with the patent office on 2003-08-07 for optical disk apparatus wherein recording clock signal is stopped being supplied to semiconductor laser drive circuit on optical pickup during reproduction operation.
Invention is credited to Asada, Akihiro, Hoshino, Takashi, Kaku, Toshimitsu, Kurebayashi, Masaaki.
Application Number | 20030147316 10/376631 |
Document ID | / |
Family ID | 27663387 |
Filed Date | 2003-08-07 |
United States Patent
Application |
20030147316 |
Kind Code |
A1 |
Asada, Akihiro ; et
al. |
August 7, 2003 |
Optical disk apparatus wherein recording clock signal is stopped
being supplied to semiconductor laser drive circuit on optical
pickup during reproduction operation
Abstract
According to the present invention, in an optical disk apparatus
constructed to supply signals for controlling a semiconductor laser
drive circuit provided to an optical pickup from a signal
processing circuit through a flexible cable, the semiconductor
laser drive circuit is so constructed as to generate a drive
current signal for the semiconductor laser on the basis of a binary
signal and a clock signal which are supplied from the signal
processing circuit through the flexible cable and the signal
processing circuit is so constructed as to supply the clock signal
during recording of data and stop the supply of the clock signal
during reproduction of data.
Inventors: |
Asada, Akihiro;
(Yokohama-shi, JP) ; Kaku, Toshimitsu;
(Hitachinaka-shi, JP) ; Hoshino, Takashi;
(Yokohama-shi, JP) ; Kurebayashi, Masaaki;
(Yokohama-shi, JP) |
Correspondence
Address: |
ANTONELLI TERRY STOUT AND KRAUS
SUITE 1800
1300 NORTH SEVENTEENTH STREET
ARLINGTON
VA
22209
|
Family ID: |
27663387 |
Appl. No.: |
10/376631 |
Filed: |
March 3, 2003 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10376631 |
Mar 3, 2003 |
|
|
|
09463007 |
Jan 19, 2000 |
|
|
|
6552987 |
|
|
|
|
09463007 |
Jan 19, 2000 |
|
|
|
PCT/JP99/04114 |
Jul 30, 1999 |
|
|
|
Current U.S.
Class: |
369/47.3 ;
369/59.11; G9B/7.01; G9B/7.018; G9B/7.099 |
Current CPC
Class: |
G11B 7/126 20130101;
G11B 7/0045 20130101; G11B 7/005 20130101 |
Class at
Publication: |
369/47.3 ;
369/59.11 |
International
Class: |
G11B 007/0045 |
Claims
1. An optical disk apparatus comprising: a semiconductor laser
drive circuit having LD recording drive current waveform generating
means for generating a recording drive current waveform for a
semiconductor laser by using a clock signal chCLK as an operation
clock when recording information on a recording medium and
reproduction drive current supply means for supplying a
reproduction drive current to the semiconductor laser when reading
the information from the recording medium; recording clock supply
means for supplying said clock signal chCLK to said semiconductor
laser drive circuit; recording/reproduction mode control means for
controlling recording/reproducing operation of said semiconductor
laser drive circuit; and clock stop means for stopping the supply
of the clock signal chCLK from said recording clock supply means to
said semiconductor laser drive circuit when the output of said
recording/reproduction mode control means designates a reproduction
operation.
Description
TECHNICAL FIELD
[0001] The present invention relates to a technique of recording
and reproducing information on and from an optical disk
representing a recording medium, and more particularly, to an
information recording and reproducing technique which can prevent
S/N degradation in a reproduction system due to cross talk with the
reproduction system caused by circuit operation in a recording
system when the information (inclusive of address information
recorded on the recording medium in advance) is read out of the
recording medium.
BACKGROUND ART
[0002] In the field of products concerning the optical disk such as
CD, DVD and the like, an increase in capacity of the optical disk
and an increase in speed of data transfer in an optical disk
apparatus have recently been desired more and more. Also, with the
capacity of the optical disk increased, mark and space
(corresponding to 1, 0 of information) to be formed on the optical
disk are required to be finer and formation of such fine mark and
space is required in the optical disk apparatus.
[0003] In order to form accurate and fine mark and space, one mark
recording waveform is required to have a multi-pulse form in a
drive current waveform for a semiconductor laser during recording
and a pulse position or pulse width at the mark start end and a
pulse position or pulse width at the mark termination end must be
controlled adaptively in accordance with a mark length of its own
and an adjoining space length. For example, in a DVD-RAM, the
aforementioned adaptive control of the pulse position or pulse
width is required to be performed in T/16 to T/32 steps (T being a
minimum unit for determining the mark and space lengths and
corresponding to the period of a so-called channel clock
chCLK).
[0004] Further, the drive current waveform is also needed to be
quaternary in contrast to the conventional binary and so has become
complicated. In addition, with the data transfer speed increased,
the frequency of the aforementioned drive current waveform has
become higher.
[0005] As the capacity and data transfer speed increase in this
manner, current at multiple-valued levels supplied to the
semiconductor laser must be switched at a high speed. To assure
such a high-speed current switching characteristic as above (rise
characteristic: Tr characteristic and fall characteristic: Tf
characteristic of the drive current), it is preferable that the
semiconductor laser drive circuit be disposed in the proximity of
the semiconductor laser.
[0006] To meet this requirement, a conventional semiconductor laser
drive circuit is so constructed as to have a plurality of current
sources at least one of which is externally selected to drive the
semiconductor laser. Therefore, as the drive current waveform has
multiple-valued levels, the number of control signal lines for
selecting the current source increases. Further, when the
semiconductor laser drive circuit is carried on an optical pickup,
control signals are supplied through a flexible cable, facing a
difficulty that because of dullness of the control signal waveforms
and the difference (skew) in delay amount between control signals,
the accurate drive current waveform cannot be obtained.
[0007] As an optical disk apparatus for solving the difficulty as
above, the present applicant has proposed an optical disk apparatus
described in Japanese Patent Application No. 10-206083.
[0008] A semiconductor laser drive circuit shown in Japanese Patent
Application No. 10-206083 is comprised of drive waveform
information memory means for storing one or more information of
drive waveform which drives a semiconductor laser in compliance
with a binary recording signal (for example, NRZ signal) to be
recorded on a recording medium, drive waveform decoding means for
decoding the drive waveform on the basis of the information stored
in the drive waveform information memory means, means for
generating an address for selecting the drive waveform information
of the drive waveform information memory means on the basis of the
binary recording signal, control means for storing the externally
supplied drive waveform information in the drive waveform
information memory means, and n-multiplying means (so-called PLL)
for n-multiplying a clock signal CLK supplied through a flexible
cable to deliver a channel clock signal chCLK and supplying the
channel clock signal as operation clock signal for the address
generation means and the drive waveform decoding means.
[0009] The drive waveform decoding means generates timing signals
for N equal division (for example, 16 or 32 equal division in the
DVD-RAM) of the period T of the chCLK by using a delay line on the
basis of the channel clock signal chCLK delivered out of the
n-multiplying means, thus permitting the aforementioned control of
the pulse width or pulse position.
[0010] With this construction, when the drive waveform information
is stored in the drive waveform information memory means in advance
through the control means, the drive current waveform is generated
during recording by supplying the binary recording signal (NRZ),
the clock signal CLK and a signal WRgate for control of the
recording or reproducing operation mode to the semiconductor laser
drive circuit carried on the optical pickup through the flexible
cable, so that the semiconductor laser can be driven nearby and the
difficulty of the conventional example that the drive current
waveform is distorted owing to the dullness or skew of the control
signals on the flexible cable can be eliminated to thereby assure
desired Tr and Tf characteristics.
[0011] In case the multiplying number n of the n-frequency means is
set to 4, the frequency of the clock signal CLK equals 1/4 of the
chCLK and as compared to the conventional example (the current
source selecting signal having the same frequency as chCLK must be
supplied), the frequency of the control signals on the flexible
cable can be reduced to 1/4 as compared to the conventional example
and the EMI generated from the flexible cable can be reduced. To
add, in the DVD-RAM, the frequency of the NRZ signal (repetition of
3T length mark and 3T length space gives a maximum frequency) is
1/6 of the channel clock signal chCLK.
[0012] As the capacity of the optical disk increases (densifying),
however, the level of the reproduction signal for reading
information from the recording medium decreases and for the sake of
assuring reliability of reproduction data, the influence such as
cross talk from the recording circuit system to the reproduction
circuit system must be more decreased. The optical pickup carries
photodetectors for detecting a reflection light beam from the
optical disk and I-V amplifiers for converting output currents of
the photodetectors to voltages, and outputs of the amplifiers are
supplied to a read channel LSI and the like through the flexible
cable. Accordingly, the influence of the crosstalk from the
recording circuit system to the reproduction circuit system must be
reduced on the flexible cable to prevent degradation of the
reproduction S/N.
[0013] Especially, when a sector is defined as a unit of recording
(storage of 2 Kbyte user data) as shown in a DVD-RAM (2.6 GByte)
illustrated at (1) in FIG. 4 and physical address information of
each sector in the form of pits is recorded on the head of each
sector (this area is called PID), the PID must be reproduced sector
by sector to confirm the address and then data to be recorded on a
user data area of each sector must be recorded. In other words,
even during recording of data, not only recording of data is
carried out but also recording and reproduction of data is carried
out repetitively.
[0014] When, as in the case of the semiconductor laser drive
circuit constructed as above, the supply of clock signal CLK to the
semiconductor laser drive circuit by way of signal lines such as
the flexible cable (hereinafter simply referred to as "flexible
cable") is kept even during PID reproduction as shown at (4) in
FIG. 4 by taking stability of the frequency of the clock signal
chCLK (output signal of the n-multiplying means) during user data
recording following the PID into consideration, EMI of the clock
signal CLK on the flexible cable (unwanted radiation emitted by the
clock signal on the flexible cable) runs in a read signal (at (5)
in FIG. 4) on the same flexible cable or on a flexible cable of the
separately provided photoelectric conversion circuit to cause
crosstalk, giving rise to a problem that the S/N of the
reproduction signal is degraded.
[0015] An object of the present invention is to decrease leakage of
the EMI of the clock signal necessary for recording of data to the
reproduction signal and degradation of the S/N of the reproduction
signal due to crosstalk and to suppress an increase of the EMI
level which causes the S/N degradation of the reproduction
signal.
DISCLOSURE OF INVENTION
[0016] To accomplish the above object, according to the present
invention, an optical disk apparatus comprises a semiconductor
laser drive circuit having LD recording drive current waveform
generating means for generating a recording drive current waveform
for a semiconductor laser by using a clock signal chCLK as
operation clock when recording information on a recording medium
and reproduction drive current supply means for supplying a
reproduction drive current to the semiconductor laser when reading
the information from the recording medium, recording clock supply
means for supplying the clock signal chCLK to the semiconductor
laser drive circuit, recording/reproduction mode control means for
controlling recording/reproducing operation of the semiconductor
laser drive circuit, and clock stop means for stopping the supply
of the clock signal chCLK from the recording clock supply means to
the semiconductor laser drive circuit when the output of the
recording/reproduction mode control means designates reproducing
operation.
[0017] Also, to accomplish the above object, according to the
present invention, an optical disk apparatus comprises a
semiconductor laser drive circuit having multiplying means for
providing a clock signal chCLK which is n times (n being positive
integer) the frequency of a clock signal CLK, LD recording drive
current waveform generating means for generating a recording drive
current waveform for a semiconductor laser by using the clock
signal chCLK as operation clock when recording information on a
recording medium and reproduction drive current supply means for
supplying a reproduction drive current to the semiconductor laser
when reading the information from the recording medium, recording
clock supply means for supplying the clock signal CLK to the
semiconductor laser drive circuit, recording/reproduction mode
control means for controlling recording/reproducing operation of
the semiconductor laser drive circuit, and clock stop means for
stopping the supply of the clock signal CLK from the recording
clock supply means to the semiconductor laser drive circuit when
the output of the recording/reproduction mode control means
designates reproducing operation.
BRIEF DESCRIPTION OF DRAWINGS
[0018] FIG. 1 is a diagram showing construction of a first
embodiment of the invention.
[0019] FIG. 2 is a diagram showing construction of a second
embodiment of the invention.
[0020] FIG. 3 is a diagram showing construction of a PLL in the
second embodiment.
[0021] FIG. 4 is a diagram showing behavior of crosstalk of a
recording clock with a reproduction system.
[0022] FIG. 5 is a diagram showing operation timings in the first
embodiment.
[0023] FIG. 6 is a diagram showing operation timings in the second
embodiment.
BEST MODE FOR CARRYING OUT THE INVENTION
[0024] Embodiments of the present invention will be described
hereunder with reference to the drawings.
[0025] (1) First Embodiment
[0026] (1. 1) Construction of First Embodiment
[0027] Construction of the first embodiment of the present
invention is shown in FIG. 1.
[0028] A semiconductor laser drive circuit 1 drives a semiconductor
laser diode 2 and an LD output light beam 3 is emitted to an
optical disk (not shown) representing a recording medium. A disk
reflection light beam 4 representing a reflected light beam of the
LD output light beam 3 emitted to the optical disk is detected by
photodetectors 51 of a photoelectric conversion circuit 5 and
current signals corresponding to a quantity of the reflected light
beam are generated. Output currents of the photodetectors 51 are
converted into voltage signals by means of I-V amplifiers 52 of the
photoelectric conversion circuit 5. The photoelectric conversion
circuit 5 delivers the voltage signals as output signals (Va, Vb .
. . Vh). Wired in a flexible cable 6 are control signal lines of a
digital signal processor (DSP) 7 for controlling the semiconductor
laser drive circuit 1 and output signal lines of the photoelectric
conversion circuit 5. A read channel circuit 8 processes the
voltage signals from the photoelectric conversion circuit 5 and
supplies them to the DSP 7.
[0029] The semiconductor laser drive circuit 1 has LD recording
drive current waveform generating means 11 for generating a
semiconductor laser drive current waveform during recording on the
basis of a binary recording signal NRZ, a control signal WRgate for
control of a recording/reproducing operation mode and a clock
signal CLK, a serial interface circuit 16 for supplying drive
waveform information 17 necessary for generation of the
semiconductor laser drive waveform to the LD recording drive
current waveform generating means 11, a read APC amplifier 12 for
current amplification of a drive current Lin supplied from the DSP
7, a high frequency modulation circuit (HFM) 13 for supplying a
high frequency current to the semiconductor laser 2 during
reproduction, and adder means 14 for adding output currents of the
LD recording drive current waveform generating means 11, read APC
amplifier 12 and HFM 13 and supplying the sum to the semiconductor
laser diode 2.
[0030] The DSP 7 has recording clock supply means 72a for supplying
a recording clock to the semiconductor laser drive circuit 1,
recording/reproduction mode control means 71 for controlling the
mode of recording/reproducing operation of the semiconductor laser
drive circuit 1, and clock stop means 73 for stopping the supply of
the recording clock signal CLK from the recording clock supply
means 72a to the semiconductor laser drive circuit when the output
signal WRgate of the recording/reproduction mode control means 71
designates the reproduction mode. Also, the DSP 7 supplies to the
serial interface circuit 16 an SEN signal for rendering the serial
interface circuit 16 operative, a clock signal SCLK for the serial
interface circuit 16 and a data signal SDIO for the serial
interface circuit 16 so as to control the serial interface circuit
16.
[0031] The semiconductor laser drive circuit 1, semiconductor laser
diode 2 and photoelectric conversion circuit 5 are carried on an
optical pickup. The optical pickup can be moved in a radial
direction of the optical disk in compliance with a recording
position (address) and a reproduction position (address) when
recording or reading on or from the optical disk is carried out.
The control signals for the semiconductor laser drive circuit 1 are
supplied from the DSP 7 through the flexible cable 6 as described
previously. The output signals of the photoelectric conversion
circuit 5 are supplied to the read channel circuit 8 through the
flexible cable 6 as described previously.
[0032] (1. 2) Operation of First Embodiment
[0033] Operation of the first embodiment and details of each
component will be described hereunder.
[0034] Operation of an optical disk apparatus of the present
embodiment is controlled by the output signal WRgate of the
recording/reproduction mode control means 71. When the control
signal WRgate is L (recording mode designation), recording
operation is effected and when H (reproduction mode designation),
reproducing operation is effected.
[0035] (1. 2. 1) Generation of Control Signal WRgate
[0036] The control signal WRgate is generated by the DSP 7 on the
basis of a PID (Physical Identification Data) section detecting
signal, which is detected by the read channel circuit 8 on the
basis of the output signals of the photoelectric conversion circuit
5 and delivered out of the read channel circuit 8, and a wobble
signal due to wobble of the recording track.
[0037] A detailed description is given of a method for detection of
the PID section and wobble signal in literature (1): NIKKEI
ELECTRONICS (last volume), 1997.10.20 (no. 701), pages 178 to 182
fully explained by a planner of the whole aspect of DVD-RAM
standards and in FIGS. 17 to 20 of the literature. The literature
(1) describes the PID section as a header section and the PID
section detecting signal as an address detection signal.
[0038] In the case of a DVD-RAM (2.6 Gbyte) format, the PID is
divided into two as shown in FIG. 20 of the literature, the first
half (headers 1, 2) being so disposed as to be 1/2 track width
displaced toward the outer periphery (or inner periphery) from the
recording track (data recording area) and the second half (headers
3, 4) being so disposed as to be 1/2 track width offset toward the
inner periphery (or outer periphery). The recording track (data
recording area) is formed in a wobble form and the wobble proceeds
at a cycle of 232 cycle ({fraction (1/186)} of chCLK period) per
sector.
[0039] Accordingly, the tracking signal (push-pull signal)
generated on the basis of the output signal of the reproduction
circuit system 5 varies largely at the PID section. For example, on
the assumption that the outer periphery side is + side, a large
variation toward the + side occurs during the first half of the PID
and a large variation toward the - side occurs during the second
half. This behavior is indicated in FIG. 20 of the literature. By
utilizing the variation, the PID section is detected. Since the
recording track wobbles, the wobble is equivalent to an error in
the tracking signal, enabling the wobble signal to be detected.
[0040] The DSP 7 generates the control signal WRgate on the basis
of the PID section detecting signal and a chCLK signal generated by
n-multiplying of the wobble signal.
[0041] Prior to a sequential recording operation of a plurality of
sectors, the control signal WRgate is first conditioned for
reproduction to perform detection of the aforementioned PID section
and detection of the current address, address detection of PID is
carried out until a desired sector and after the desired sector has
been detected, the control signal WRgate is conditioned for
recording at recording data areas as shown at (2) in FIG. 5. Start
and termination timings for the recording data area of each sector
are determined on the basis of a coefficient of the chCLK signal
generated from the previously-described wobble signal.
[0042] (1. 2. 2) Reproducing Operation
[0043] Reproducing operation is effected when the output signal
WRgate of the recording/reproduction mode control means 71 is at a
logical high (H). At that time, in the semiconductor laser drive
circuit 1, the read APC amplifier 12 current-amplifies the
reproduction drive current Iin supplied from the DSP 7 through the
flexible cable 6 and a resulting current is added with a high
frequency current signal from the high frequency multiplexing
circuit 13 by means of the adder means 14 to drive the
semiconductor laser diode 2. The semiconductor laser diode 2 is
caused to luminesce by reproduction power so as to illuminate the
optical disk. Reflection light beam 4 from the optical disk is
guided to the photodetectors 51 and each of the photodetectors (a
to h totaling to 8) detects a quantity of reception light. Currents
corresponding to the reception light quantities of the individual
photodetectors are subjected to current-to-voltage conversion by
means of the I-V amplifiers (a to h totaling to 8 circuits)
corresponding to the photodetectors and resulting voltages
(detection signals Va to Vh in the Figure) are supplied to the read
channel circuit 8 through the flexible cable 6.
[0044] (1. 2. 3) Recording Operation
[0045] Recording operation is effected when the output signal
WRgate of the recording/reproduction mode control means 71 is at a
logical low (L).
[0046] At that time, in the semiconductor laser drive circuit 1,
the recording drive current from the LD recording drive current
generating means 11 is added with the drive current of the read APC
amplifier 12 (the same current as the reproduction drive current
during reproducing operation) at the adder circuit 14 so as to
drive the semiconductor laser diode 2.
[0047] The LD recording drive current generating means 11 generates
a recording drive current waveform corresponding to a length of a
mark to be recorded (mark length being, for example, 3T, 4T, . . .
, 11T) and a length of an adjoining space (space length being, for
example, 3T, 4T, . . . , 11T) on the basis of the binary recording
signal NRZ and clock signal CLK (in the first embodiment,
corresponding to a channel clock signal, that is, corresponding to
the period of a minimum unit of change of the NRZ signal). What
type of recording drive current waveform is to be formed is set by
the recording drive waveform information 17 supplied from the DSP 7
through the serial interface 16.
[0048] (1. 2. 4) Operation Timings
[0049] In FIG. 5, operation timings in the first embodiment are
shown. In the Figure, a format of the optical disk (disk format) is
depicted at (1), a signal waveform of the control signal WRgate is
depicted at (2), and sections (timings) at which the recording
drive current waveform (write pulse) is delivered out of the LD
recording drive current generating means 11 or adder circuit 14 are
depicted at (3). Further, in the Figure, sections (timings) at
which the recording clock signal CLK is supplied to the
semiconductor laser drive circuit 1 through the flexible cable 6
are depicted at (4), a section (timing) at which the drive current
Iin is delivered is depicted at (5) and sections at which the PID
(physical ID recorded with physical address information of each
sector) is reproduced and the output signals (Va, Vb . . . Vh) of
the respective I-V amplifiers 52 are supplied to the read channel
circuit 8 through the flexible cable 6 are depicted at (6).
[0050] Like the DVD-RAM disk, for example, this disk format has a
unit of recording defined by a sector unit and each sector includes
a field (user data area (DATA rewritable) having a length of about
2418.times.16T) for recording 2048-byte user data and an error
correction sign, an area (PID having a length of 128.times.16T) on
which physical address information on the disk of each sector is
recorded (in the form of pits) in advance and an area (GAP being,
more strictly, comprised of a gap and a guard area and having a
length of about 30.times.16T) serving as a buffer area between the
two areas.
[0051] When user data is recorded on the sector N, the PID of the
sector N is reproduced to confirm a physical address of the sector
to be recorded with data and thereafter recording is carried out.
This aims at preventing data from being recorded on an erroneous
sector and data, already recorded, from being destroyed and lost in
the case of the scheme capable of recording at random in a unit of
sector (this realizes the capability of random access in recording
and reproduction inherent in the optical disk) in contrast to the
conventional scheme for sequential data recording (for example, the
recording method such as CD-R). So to speak, even in the recording
mode, in addition to mere effectuation of recording, recording of
data and reproduction of PID are repeated.
[0052] In compliance with the disk format described above, the
recording/reproduction mode control means 71 delivers, as shown at
(2) in the Figure, a control signal WRgate which designates the
reproduction mode (read) at the PID section and the recording mode
(write) at the GAP area and user data area ("DATA rewritable" at
(1) in the Figure).
[0053] The clock stop means 71 responds to the mode designated by
the control signal WRgate to control the supply/stop of the
recording clock CLK to be supplied to the semiconductor laser drive
circuit 1. As shown at (4) in the Figure, the supply of the
recording clock CLK is stopped when the WRgate is H (reproduction
mode) and the recording clock CLK is supplied when L (recording
mode).
[0054] The LD recording drive current waveform generating means 11
generates a recording drive current waveform on the basis of the
supplied recording clock CLK and binary recording signal NRZ and
the generated waveform is then added with the drive current Iin,
thereby driving (out write pulse) the semiconductor laser diode 2
at timings (user data area) shown at (3) in the Figure to form mark
and space on the disk.
[0055] In the operation timings as above, during a period for
delivery of the output signal shown at (6) in the Figure, that is,
during the PID reproduction period, the delivery of the recording
clock CLK is stopped, with the result that the influence of EMI of
the recording clock upon the drive current Iin and output signals
(Va, Vb . . . Vh) can be decreased as compared to the case where
the delivery of the recording clock CLK keeps and as compared to
the case where the delivery of the binary recording signal NRZ
keeps (out write pulse).
[0056] (1. 3) Effects of First Embodiment
[0057] As described above, in the first embodiment, the recording
clock CLK is stopped during PID reproduction to bring about the
following effects.
[0058] a) Since crosstalk of the recording clock CLK due to EMI
with the output signals (Va, Vb . . . Vh) of the photoelectric
conversion circuit 5 can be reduced on the flexible cable 6, the
error rate of data reproduction such as PID can be reduced.
[0059] b) Crosstalk of the recording clock CLK due to EMI with the
drive current Iin determining the drive current for the
semiconductor laser diode during reproduction can be reduced on the
flexible cable 6, variation due to the crosstalk in the output
light beam of the semiconductor laser diode 2 can be reduced and
consequently, S/N degradation in the reproduction signal can be
prevented to thereby reduce the error rate of data reproduction
such as PID.
[0060] c) Since the crosstalk of the recording clock with the
reproduction signal system can be reduced on the flexible cable 6
as described above, the recording clock signal, reproduction
circuit system output signals and drive current signal Iin can be
arranged in close proximity to each other on the flexible cable and
the width of the flexible cable can be reduced to permit reduction
in size of the apparatus.
[0061] (2) Second Embodiment
[0062] (2. 1) Construction of Second Embodiment
[0063] Construction of a second embodiment of the present invention
is shown in FIG. 2. Components having the same function as those in
FIG. 1 are designated by the same reference numerals.
[0064] Structurally, the present embodiment differs from the
optical disk apparatus according to the first embodiment in that
there is provided multiplying means (phase locked loop) 15 for
multiplying a clock signal CLK supplied by way of the clock stop
means 73 to generate a channel clock signal chCLK and supplying it
to the LD recording drive current waveform generating means 11.
[0065] Construction of the multiplying means (PLL) 15 is shown in
FIG. 3. A frequency division circuit 151 n-divides the frequency of
the output signal chCLK of a VCO (voltage controlled oscillator)
156. A phase difference detection circuit 152 detects a phase
difference between an output signal CLKO of the frequency division
circuit 151 and the recording clock signal CLK supplied by way of
the clock stop means 73. A charge pump circuit 153 generates a
voltage)corresponding to the detected phase difference of the phase
difference detection circuit 152. An LPF (low-pass filter) 154
smooths the output signal of the charge pump circuit 153. A hold
circuit 155 holds an output value of the LPF 154 when the control
signal WRgate is H (reproduction mode). The VCO 156 changes its
oscillation frequency in compliance with the output value of the
LPF 154 supplied through the hold circuit 155. The output signal of
the VCO 156 is supplied as the channel clock signal chCLK to the LD
recording drive current waveform generating means 11.
[0066] (2. 2) Operation of Second Embodiment
[0067] A multiplying number n of the multiplying means (PLL) 15 is
set by the DSP 7 through the serial interface 16. Recording clock
supply means 72b responds to the multiplying number n information
18 to deliver a recording clock CLK having a frequency which is 1/n
of the frequency fchCLK of the channel clock chCLK. The multiplying
means (PLL) 15 generates the channel clock chCLK by n-multiplying
the frequency of the recording clock CLK and supplies it to the LD
recording drive current waveform generating means 11. The LD
recording drive current waveform generating means 11 generates a
recording drive current waveform on the basis of the binary
recording signal NRZ and the channel clock signal chCLK supplied
from the multiplying means (PLL) 15. Then, the thus generated
current is added with the drive current Iin to drive the
semiconductor laser driver 2
[0068] (2. 2. 1) Operation Timings
[0069] Operation timings in the second embodiment are shown in FIG.
6. In the figure, a format of the optical disk (disk format) is
depicted at (1) in FIG. 6, the control signal WRgate is depicted at
(2) in FIG. 6 and sections (timings) at which the recording drive
current waveform (write pulse) is delivered out of the LD recording
drive current waveform generating means 11 or adder circuit 14 are
depicted at (3) in FIG. 6. These are the same as the operation
timings in the first embodiment. In the Figure, a timing for
operation of the multiplying means (PLL) 15 is depicted at (4) in
FIG. 6 and sections (timings) at which the recording clock CLK (in
the second embodiment, the frequency of the CLK is 1/n of the
channel clock chCLK) is supplied to the semiconductor laser drive
circuit 1 through the flexible cable 6 are depicted at (5) in FIG.
6. In the Figure, a section (timing) at which the drive current Iin
is delivered is depicted at (6) in FIG. 6 and sections (timings) at
which the PID is reproduced and the output signal of each I-V
amplifier 52 is supplied to the read channel circuit 8 through the
flexible cable 6 are depicted at (7) in FIG. 6.
[0070] When user data is recorded in a sector unit, like the first
embodiment, the recording/reproduction mode control means 71
renders the control signal WRgate H (reproduction mode) at the PID
sections and renders it L (recording mode) at the GAP and user data
area.
[0071] Like the first embodiment, the clock stop means 73 stops the
supply of the recording clock CLK from the recording clock supply
means 72b to the semiconductor laser drive circuit 1 when the
WRgate is H (reproduction mode) and supplies the recording clock
CLK to the semiconductor laser drive circuit 1 when the WRgate is L
(recording mode).
[0072] When the control signal WRgate is L (recording mode), the
multiplying means (PLL) 15 receives, as an input signal, the
recording clock CLK supplied through the clock stop means 73 as
shown at (4) in FIG. 6 and operates to cause the phase of the input
signal to coincide with that of the output signal CLKO of the
frequency division circuit 151. With the phases of the two rendered
to be coincident with each other, the output of the VCP 156
consequently becomes the channel clock chCLK which is n times the
CLK and the channel clock is supplied to the LD recording drive
current waveform generating means 11. When the control signal
WRgate is H (reproduction mode), the hold circuit 155 holds an
immediately preceding (immediately before the change of the WRgate
from L to H) output value of the LPF 154.
[0073] The oscillation frequency of the VCO 156 is controlled by
the output value of the hold circuit 155. Accordingly, during the
section at which the WRgate is H (reproduction mode), the supply of
the recording clock CLK is stopped but the oscillation frequency of
the VCO 156 holds a frequency which is substantially equal to the
frequency when the WRgate is L (recording mode).
[0074] By holding the oscillation frequency of the VCO 156 at the
PID reproduction section, pull-in of the VCO 156 to the recording
clock CLK (operation to cause the frequency division circuit output
CLKO to coincide with the frequency of the recording clock CLK and
to make the phases coincident with each other) can be effected more
speedily when the WRgate again comes into L (recording mode). The
reason for this is that the held frequency of the VCO 156 is close
to n times the recording clock CLK, in other words, the frequency
of the output CLKO of the frequency division circuit nearly equals
the frequency of the recording clock CLK and therefore the control
time for making the frequency of the CLKO coincident with the
frequency of the CLK can be shortened.
[0075] Since at the operation timings as above the delivery of the
recording clock CLK is stopped during the period shown at (6) in
the Figure in which the output signal is delivered, that is, during
the PID reproduction period as in the case of the first embodiment,
the influence of the recording clock due to EMI upon the drive
current Iin and output signals (Va, Vb . . . Vh) can be reduced as
compared to the case where the delivery of the recording clock CLK
keeps and to the case where the delivery of the binary recording
signal NRZ keeps (out write pulse).
[0076] Further, the frequency of the recording clock CLK passing on
the flexible cable 6 can be reduced as compared to that in the
first embodiment and consequently, the influence of the recording
clock CLK due to EMI can be reduced by itself.
[0077] (2. 3) Effects of Second Embodiment
[0078] As described above, in the second embodiment, the following
effects can be brought about in addition to those attained by the
first embodiment.
[0079] d) Since the recording clock CLK is n-multiplied on the side
of the semiconductor laser drive circuit 1 (optical pickup side) by
means of the multiplying means (PLL) 15, the frequency of the
recording clock CLK on the flexible cable 6 can be reduced to 1/n.
Accordingly, the level of unwanted radiation (EMI) emitted from the
flexible cable 6 can be reduced as compared to that in the first
embodiment, so that crosstalk with the drive current Iin during
data recording can be reduced as compared to that in the first
embodiment. Namely, the recording drive current waveform can be
generated with higher accuracy in the present embodiment than in
the first embodiment.
[0080] e) By holding the oscillation frequency of the VCO 156 at
the reproduction mode section, the oscillation frequency of the VCO
156 can be pulled in to n times the frequency of the recording
clock CLK more speedily at the time that the recording mode starts,
with the result that variation of the channel clock chCLK at the
user data area can be reduced to thereby prevent degradation of
reliability of the recording data.
INDUSTRIAL APPLICABILITY
[0081] In the optical disk apparatus of the present invention, S/N
degradation in the reproduction signal can be reduced. Further, an
increase in the EMI level which causes the S/N degradation in the
reproduction signal can be suppressed.
[0082] Especially, in an optical disk apparatus in which recording
of data is carried out by reading address information on the
optical disk and confirming the recording position, the error rate
of reproduction of data such as address information can be reduced
and hence reliability of data recording can be promoted.
* * * * *